I was looking here http://search.petfinder.com/petnote/displaypet.cgi?petid=8295508 and saw this: Why do they crop their ears? ....
A kitty that is feral has the tip of its ear cropped. Many times feral cats are spayed/neutered and returned to the place where they were living free. The cropped ear can tell someone trapping cats to neuter, from a distance, that this cat has been altered and can not reproduce, tested negative for feline leukemia (and usually has had vaccine) has had at least basic shots and rabies vaccine too. In otherwords, it tells people who work with ferals, that this cat has been taken care of at least once. Sometimes when cats are feral, they get to where they trust people and can become quite domesticated...OR a cat that was part of a family, got dumped in a place with a bunch of feral cats, was trapped, and had vet care - then after their surgery, it is realized that someone once owned this animal and they have little to do to make them placeable for adoption. (which was the case in the cat above that you mentioned) The cropping is done while they are under anesthesia and from what I have been told the kitty doesn't feel too much in the way of pain as they have pain medication for their surgery. . . I've met a few kitties whome people adopted, who had a ear cropped - they don't seem to mind you touching it.
I have a feral colony done by catnip. It is always the left ear, and normally the tip. I have one they took about 1/2 the ear off. It helps the shelters know as well.... and animal control can sometimes look the other way in certain situations (since they know they are altered.) We have had some clipped ears come by the shelter that were definitely not feral anymore (some people will sneak a non feral cat into catnip for the free spay, but sometimes they just become friendly.)
